Studies On The Starch-Like Granules Co-Accumulated With Polyhydroxybutyrate In Spirulina Platensis

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Date
2007-06
Authors
Peng, Yew Saw
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Spirulina platensis is capable of synthesizing small amount of polyhydroxyalkanoate (PHA) under nitrogen starvation condition. Gas chromatography (GC) analysis revealed that about 10 % PHA of the cell dry weight (COW) was accumulated under mixotrophic culture condition containing 0.5% (w/v) of sodium acetate. However, Nile blue A stained cells showed the presence of large quantities of granules in the cell cytoplasm when viewed under fluorescent microscope. The qualitative observation was in contrast to the quantitative GC analysis which suggested that not all the fluorescent granules are PHAs. It was hypothesized that S. p/atensis co-accumulated other storage products that were stained with Nile blue A along with PHA under nitrogen starvation condition. Closer observation by transmission electron microscopy (TEM) revealed the presence of starch-like granules along with PHA granules. Analysis of several types of commercial starches confirmed that starch granules could be stained by Nile blue A although the intensity of the fluorescence was lower than for PHA granules. In order to further characterize the starch-like granules, large genomic DNA fragments of S. platensis were randomly cloned into E. coli 817-1 and resulting recombinants were screened for Nile blue A XV positive characteristic. One such recombinant E. coli was able to accumulate morphologically similar granules. GC and PHA synthase activity analyses confirmed that these are not PHA granules. GC-MS analysis revealed that the recombinant E. coli accumulated starch-like compound consisting of glucose monomers. The granules exhibited birefringence under polarized light, which is a characteristic of semi-crystalline starch granules. This study showed for the first time that S. platensis co-accumulated PHA and starch-like granules during nitrogen starvation. Suppression of the starch-like granule biogenesis might produce a higher PHA accumulation in S. platensis.
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Spirulina Platensis
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